1. Field of the Invention
The present invention relates to a camera equipped with a motion compensation device to suppress image blur resulting from motion of the camera and, more particularly, a camera which performs motion compensation for sequential photographs by continuously detecting motion until the final photograph is taken.
2. Description of the Related Art
Optical systems project an image onto an image plane. Conventional image blur suppression devices suppress, or reduce, blurring of the image. A motion compensation device is a type of image blur suppression device, and compensates for motion incident upon the optical system. Motion is typically imparted to the optical system by vibrations in the optical system, or in a surrounding holding member. In general, conventional motion compensation devices cause a compensation lens to shift counter to the motion of the optical system so as to shift the image projected by the optical system relative to the optical system. Conventional cameras use a motion compensation device to suppress image blur resulting from motion of the camera. Such motion is typically caused by hand tremors of the photographer.
In a camera equipped with a motion compensation device, a motion sensor detects the amount of motion affecting the camera by detecting the angular velocity or acceleration produced by the motion. The motion sensor then produces an output signal in correspondence with the amount of detected motion. The direct current component of the sensor output is eliminated, and the alternating current component of the sensor output is received by a sensor circuit. The sensor circuit determines the amount of motion from the amplitude of the alternating current component of the motion sensor output signal.
The output signal produced by the motion sensor is generally very small. Therefore, the sensor circuit includes an amplifier to amplify the output signal of the motion sensor. To improve the motion detection sensitivity of the motion sensor, the sensor circuit may increase the power source voltage supplied to the amplifier. However, the amount of power which can be supplied is limited.
To accurately detect the amount of motion affecting the camera, a reference level of the amplified signal (that is, the signal level when there is no motion affecting the camera) is detected. For example, the reference level can be derived by taking an average of the output of the sensor circuit amplifier during a time period when there is a margin in relation to the motion cycle. However, as previously described, the direct current component of the motion sensor output signal is eliminated. Therefore, the reference level of the amplified signal cannot be easily detected. Poor detection of the reference level produces inaccurate motion compensation due to errors in the reference level. The precision of the reference level is improved as the time period is increased. In other words, the precision of the reference level is improved when the average of the output of the sensor circuit amplifier is taken over a longer period of time.
Further, immediately after being started, the motion sensor requires a small amount of time until its output signal stabilizes. However, when executing a series of continuous photographs, the power source of the motion sensor is turned ON and OFF for each individual photographic operation, thereby requiring a new determination of the reference level for each photographer. This conventional approach does not utilize the reference level determined for the proceeding photograph.